Q: keyboard light on my macbook pro

What is it doing or not doing???

reset the  SMC

http://support.apple.com/kb/ht3964

What happens if you cover the light sensor with your hand- right next to the iSight camera on top?

http://support.apple.com/kb/HT4882

Which MacBook Pro do you have and what OS are you running, it says OS X (10.5.1)?

You tell me did your 2006 ever have backlit keyboard??

Late 2006 17-inch: 2.33GHz(MA611LL/A) did have the illuminated keyboard.

The built-in F-key functions are alternatives to the standard F1 through F12 keys. If you choose this option try the function key fn + F5 F6

Is the fn key box checked in that Keyboard preference pane?

Did you try the fn key combination?

I am showing the Late 2006 17-inch: 2.33GHz did have the illuminated keyboard.

http://support.apple.com/specs/

I have two conflicting data sheets here so on 2006 2007 start date for backlit so

We are still shooting in the dark unless you supply a model number http://support.apple.com/specs/

http://support.apple.com/kb/SP24

There is some talk of it being an option? But this spec sheet with your model indicates backlit.

I would take to the genius bar  at your Apple store for further review.